1. Field of the Invention
This invention relates to a spirometer, particularly a fluidic oscillator spirometer, for measuring respiratory flow rates.
2. Description of Related Art
In the United States, the American Thoracic Society (ATS) sets guidelines and standards for treatment of people with respiratory disease. ATS guidelines suggest that lung function should be monitored regularly for patients with known respiratory disease. Patients use daily home monitoring of peak flow to periodically check respiratory flow.
Patients and doctors use three main types of conventional devices to assess lung function: standard spirometers, monitoring spirometers, and peak flow meters. Standard spirometers, often used in a medical office, provide the most reliable results. However, standard spirometers are relatively expensive and require significant user training for proper operation. Standard spirometers are not portable and often require the user to own a computer to operate the spirometer.
Standard spirometers produce the most accurate results when assessing lung function. However, the cost of a standard spirometer ranges from about $ US 2,000 to about $ US 10,000, and thus are not readily available or practical for daily home use. Also, standard spirometers can become less accurate as respiratory flow rates become relatively low. Patients with respiratory disease often can achieve only relatively low flow rates during exhalation, and thus the standard spirometer operates in a less accurate range.
The standard spirometer uses a pneumotachigraph, in which fluid flows through hundreds of small tubes and the flow rate is determined by measuring a pressure drop across the tubes. In pneumotach spirometers, air that flows through the tubes is moist and often full of mucus debris. The tubes can become clogged with the mucus debris, which further reduces the accuracy of the standard spirometer. Also, such standard spirometers are difficult to clean and sterilize, primarily because they must be disassembled for thorough cleaning.
Standard spirometers require daily calibration of a pressure drop across the pneumotach. The calibration process is time-consuming and awkward.
Monitoring spirometers are relatively new for pulmonary medicine. The corresponding devices are relatively small and thus portable, and more conducive for home monitoring uses. However, monitoring spirometers are less accurate than standard spirometers. Most monitoring spirometers are used to manually record spirometry values which are typically displayed, for example on a relatively small liquid crystal display. Also, manual recording of spirometry values requires diligent compliance on a daily routine. Because home compliance is a significant problem with daily physical activities at home routines, manually recorded results are often inaccurate and result in an incorrect diagnosis.
Most monitoring spirometers simply report spirometry values. A common measurement in lung function testing is Forced Expiratory Volume in one second (FEV1.0), which relates to the volume of air that a patient can forcefully exhale during the first second of exhalation. However, information contained in the FEV1.0 value is not as useful to the physician as a graph of the time-volume curve for each day. The time-volume curve can convey to the physician the nature of the disease but in contrast, a simple number value cannot convey such information. Most standard spirometers produce a time-volume curve but most monitoring spirometers do not produce a time-volume curve.
Conventional peak flow meters can be used to assess lung function. Peak flow meters are relatively inexpensive, portable devices that set the current standard for home monitoring. Peak flow meters measure only a maximum flow rate that a patient can achieve during forceful exhalation. The maximum flow rate measurement provides relatively little useful diagnostic information. However, some physicians believe that because diagnostic results obtained using a measure of peak flow rate are not worth the time, effort and expense involved, patients may avoid use of peak flow meters when performing daily tests.
Some pulmonary physicians believe that daily monitoring of lung function is potentially as beneficial to individuals with lung disease as daily monitoring of blood sugar levels is to individuals with diabetes mellitus, particularly if the respiratory monitoring device can provide diagnostically useful information in a reliable form. It is apparent that there is a need for a spirometer that is relatively small, portable, inexpensive and that can accurately measure, process and record respiratory flow rates.